Observational and theoretical studies on ecology and material cycles influence of overturning deficiency

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Air temperature around Lake Biwa has increased by 1℃ during past 20 years due to the global warming. This is almost 5 times as the average increase of the world. Such rapid increase of the air temperature is resulting in more stable and monotonous climate around Lake Biwa. Also it induced some changes in the hypolimnion of Lake Biwa. The increase of water temperature, nitrate, chloride and the decrease of dissolved oxygen, fish production and pH can be listed. The mutual relationship among these changes is not well clarified, but we understand that there exist any correlation. Also we have measured dissolved oxygen near lake bottom, and we found that the lowest concentration of dissolved oxygen in the hypolimnion of Lake Biwa strongly depends on the overturning and the cold the cold water intrusion in winter time. As the winter in 2004 was the warmest in the record, we worry very low dissolved oxygen may occur this autumn.